The Cathode Ray Tube
Desktop Monitors
Often referred to as a monitor the display is the most used output device on a computer. The display provides instant feedback by showing text and graphic images to you as you work or play. Most desktop displays use a cathode ray tube (CRT) to display these images. In monitors based on CRT technology, the refresh rate is the number of times that the image on the display is drawn each second. Refresh rates are very important because they control flicker, and you want the refresh rate as high as possible. Here is how the CRT works
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The Cathode Ray Tube |
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A CRT is essentially an oddly-shaped, sealed glass bottle with no air inside. The base is the monitor’s ‘screen’ and is coated on the inside with a matrix of thousands of tiny phosphor dots. Each phosphors emit different colored light. Each dot consists of three blobs of colored phosphor, Red Blue and Green.
In the ‘bottle neck’ of the CRT is the electron gun, which is composed of a cathode, heat source and focusing elements. Color monitors have three separate guns, one for each phosphor color. Combinations of different intensities of red, green and blue phosphors can create the illusion of millions of colors.Images are created when electrons, fired from the electron gun, and strike their respective phosphor blobs. When this happens, light is emitted, in the color of the individual phosphor blobs. The gun radiates electrons when the heater is hot enough to liberate electrons (negatively charged) from the cathode, which are then narrowed into a tiny beam by the focus elements. The electrons are drawn toward the phosphor dots by a powerful, positively charged anode, located near the screen.
Power consumption varies greatly with different technologies. CRTs use a lot of power, about 110 watts for a typical display. In a typical home computer setup a CRT-based monitor, accounts for over 80% of the electricity used. This is why we are utilizing the new technology of LCD and LED displays.